1. Field of the Invention
The present invention relates to an automatic focusing apparatus of a camera, and more precisely, it relates to an automatic focusing apparatus in an automatic focusing single lens reflex camera having an auxiliary light emitting device.
2. Description of Related Art
In recent single lens reflex cameras, automatic focusing devices are usually provided. Frequently, a TTL phase difference detection type of focus detecting means is provided in a single lens reflex camera to detect a focus thereof. The TTL phase difference detection type of focus detecting device calculates a deviation (amount of defocus) of an image plane from a film plane due to the phase difference between the two divided images of an object to be taken formed by a taking lens (photographing lens). The necesssary displacement of the focusing lens within the taking lens is calculated in accordance with the calculated amount of defocus so that the focusing lens is moved to the focal point through the calculated displacement by a focusing motor.
The relationship between the amount of defocus and the displacement of the focusing lens depends on the taking lens. To this end, in a conventional single lens reflex camera, the taking lens (interchangeable lens) is provided with a memory means (e.g. ROM) in which lens data peculiar to the taking lens, such as data (which will be referred to as K value data) relating to displacement of the focusing lens corresponding to the unit defocus amount. A microcomputer provided in the camera body has a data communication function in which the lens data stored in the ROM of the taking lens is read.
Recently, taking lenses in automatic focusing (AF) single lens reflex cameras have used a zoom lens in which the K value data varies in accordance with the focal length f thereof. To this end, a focal length detecting means provided on the zoom lens to detect the present focal length, and the K value data corresponding to the focal lengths is stored in the lens ROM.
However, control of the focal length detecting means and retrieval of the K value data must be carried out by the microcomputer of the camera body (body microcomputer). This increases the communication time and unduly loads the body microcomputer.
Furthermore, it is also known to emit a striped pattern of auxiliary infrared light onto the object to be taken in order to make it possible to control the automatic focusing even at a small luminance or low contrast. The body microcomputer calculates the necessary displacement of the focusing lens, based on the amount of defocus in accordance with the image formed by the auxiliary infrared light.
However, the focal length f of the taking lens varies in accordance with the wavelength of light. Accordingly, upon emitting the auxiliary infrared light, if the focusing lens is moved by a displacement corresponding to the same amount of defocus as that obtained when natural light (reference light) is used, the object could be out of focus. To move the focus lens to the correct position when the auxiliary light is used, it is necessary to adjust the amount of defocus in accordance with adjustment data, such as a shift of image plane by the auxiliary light relative to the image plane by the reference light.
However, if all adjustment data corresponding to a plurality of focal lengths is stored in the lens ROM in a known page-memory system, it is necessary to use a large capacity lens ROM, resulting in an increased load on the body microcomputer and increased operation time.